B2b Advice please (1 Viewer)

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Bustup15

LIFE MEMBER
Jun 25, 2018
1,555
3,887
Durham
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54,597
MH
Dethleffs I 7820-2
Exp
New to motorhomes 2019
It seems the general concensus for charging leisure batteries is a combination of solar and b2b.

Engine battery is between the seats (Ducato A class), leisure batteries (2*110ah) are in the garage and are about 6 metres apart.

Is the size of required cable determined by
A. The size of battery
B. The distance apart
C. Required time to charge them
D. Something else
E. Combinations of above.

Recommendations and advice welcomed

Cheers

Neil
 
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OP
Bustup15

Bustup15

LIFE MEMBER
Jun 25, 2018
1,555
3,887
Durham
Funster No
54,597
MH
Dethleffs I 7820-2
Exp
New to motorhomes 2019
It seems the general concensus for charging leisure batteries is a combination of solar and b2b.

Engine battery is between the seats (Ducato A class), leisure batteries (2*110ah) are in the garage and are about 6 metres apart.

Is the size of required cable determined by
A. The size of battery
B. The distance apart
C. Required time to charge them
D. Something else
E. Combinations of above.

Recommendations and advice welcomed

Cheers

Neil
Should have added there is also 2*100w solar but couldn't edit thread for some reason
 

Camping Gaza

Free Member
May 7, 2016
993
1,467
La Châtre, Centre-Val de Loire France
Funster No
42,958
MH
Coachbuilt Low profile
Exp
Converted a Fiat Ducato PV a while back
D....

Question is a bit vague are you wanting to know the size of the cable from your starter battery to your B2B? and then the cable size from the B2B to your battery bank?

If so you need to know the maximum amps your B2B will charge your Hab battery (or bank) ie 20a 60a etc, this will depend on the model and spec of the B2B This will all be in your instruction manual for your B2B and installation instructions re cable sizing

Size of battery for charging is of no importance, unless charge time is important. as is distance apart for charging (unless its several hundred feet!)

Solar is another matter, you will need to know the output of your solar controller to know the cable size that goes to your battery for charging. look at you manual for your solar charger to see max output in amps

In a nutshell the cable sizes are determined by amps required by the B2B and the solar charger.

If your B2B charger is say 60 amp max output to the batterys to be charged then run 60 or larger amp cable all round, inc from your starter battery to the B2B. Larger will reduce resistance over longer runs but dont go mad. (you can even run the same size cable from the solar controller to the batteries, for charging, bigger is better!)

Google 60 amp (or whatever) 12v cable for AWG sizes or mm2. can't remember off the top of my head

Make sure all is fused correctly this is so important in vehicles where chafing can occur

Use 2 cables for the circuits, red and black, Positive and negative , avoid using the chassis as an earth return because I don't know what effect it could have on your CANBUS system if you have it

Qualification... have a solar 300watt, 40 amp B2B system charging hab and cab system for 3 years all home brew no problems.
 
Last edited:
Jul 10, 2018
245
519
Worcester(U.K)
Funster No
54,848
MH
Tamar Ducato160multi
Exp
15
We used the cable size stated in the BB1260 user manual. They are an amazing bit of kit.
 

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JockandRita

LIFE MEMBER
Aug 2, 2007
11,714
154,809
Lincs/Cambs border
Funster No
49
MH
N+B Flair 8000i
Exp
Since May 05 (Ex Tuggers).
Our B2B is the older style 1250. I used 30mm square, black coloured welding cable, and marked the positive with red electricians tape at both ends, and +POS using an indelible marker. (At the time, I couldn't get a hold of red coloured cable of the same dimensions). An upside for me, was the short cable run from the B2B to the leisure batteries. The longest cable run was from the starter battery.

As a DIY'er, I was very apprehensive, erring on the side of safety, but I did my homework and research, which included speaking with nickvanbitz (extremely helpful), and with the Irish chap at Sterling themselves, again, extremely helpful.

I kept thinking, how embarrassing would it be if I got it wrong, and the ex Fireman's MH went up in a blue flash and a puff of smoke. :LOL:

Bustup15. Good luck with it Neil. (y)

Jock. :)

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May 7, 2016
7,591
12,526
West Sussex
Funster No
42,951
MH
Malibu Van 640 LE K
Exp
Since 2003
This link has some helpful advice about cable sizing. https://www.12voltplanet.co.uk/cable-sizing-selection.html
You need to avoid a voltage drop of more than 3-4%. The voltage drop depends on the Amps, size of cable and length of cable run. The link includes a very helpful voltage drop calculator. If you enter 50A, 16mm cable and 6m distance you get 5.3%, which is too high but at 3m distance the drop is down to 2.67% which is ok.
 

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